stl · medium

std::variant & std::visit

std::variant holds one of several types and remembers which via index(). std::visit dispatches to the overload for the active type. Accessing the wrong alternative throws std::bad_variant_access — safer than a raw union, which gives undefined behavior.

The code

std::variant<int, std::string, double> v = 42; // holds int, index 0
v = std::string("hi");                         // now holds string, index 1
size_t i = v.index();                          // 1

std::visit([](auto&& x) { use(x); }, v); // -> string overload
int n = std::get<int>(v);                // throws bad_variant_access

What this lesson walks through

1. 01
2. 02
3. 03
4. 04
5. 05
6. 06